Control circuit



Feb. 25, 1964 J. B. DEYSHER ETA].

CONTROL CIRCUIT Filed April 14, 1959 FUSE POWER SUPP!- Y n N 0 N w R m mW55. A m M M M Y B 3,1225% Patented Feb. 25, 199i 3,122,646 CONTRSLCllitt'lillli James B. Deysher, Ambler, and Peter E. Slavin,Philadelphia, Pm, assignors to Sperry Rand Corporation, New York, N.l.,a corporation of Delaware Filed Apr. 14, 1959, Eler. No. 8%,368 4Qlaims. (Ql. Elli-$8.5)

This invention relates to control circuits, and more particularlyrelates to means for terminating a first power supplied to an electricalcircuit upon the failure or faulty operation of a second power suppliedto such circuit.

More specifically, this invention has utility in conjunction with atransistor load circuit, having main power and bias power appliedthereto. The control circuit, as taught by this invention, terminatesthe application of the bias power to the transistor upon the failure orimproper op eration of the main power.

When the main power supplied to certain types of transistor circuitry isremoved through failure, instantaneous removal of bias voltage isdesired to prohibit destruction of transistors and diodes in thecircuitry due to overload. One method of protecting circuitry fromdestruction due to overload is to utilize a fuse together Withmechanical relays, so that, upon failure of the fuse, the mechanicalrelays remove all other voltages. However, when a fuse open-circuits, afinite amount of time elapses before other voltages are removed, due tothe release time of the mechanical relays used in such protectivecircuits. The transistor control circuit, as taught by this invention,removes instantaneously one voltage in the event of the failure ofanother voltage. The speed of switching is de termined by the time ofthe transistor turn-off and is approximately two microseconds. Thedestruction of the transistors and diodes in load circuits, therefore,is avoided.

It is an object of this invention to provide a novel bistable circuit.

It is a further object of this invention to provide a novel transistorcircuit breaker.

An additional object of this invention is to provide novel means forcontrolling one voltage by a second voltage.

Another object of this invention is to provide a novel fuse circuitwhich operates at exceedingly hish speeds.

An additional object of this invention is to provide a novel protectivecircuit for transistor devices.

In accordance with this invention, a controlled voltage is terminated bythe failure of a controlling voltage. The voltage to be controlled issupplied to the emitter of a transistor, which transistor providescontrolled voltage at its collector. The controlling voltage, togetherwith another voltage, is connected to a voltage divider. The voltagedivider is connected to the base of the transistor in a manner to biasthe transistor in a forward direction so that the potential differencebetween the base and the emitter is approximately one volt. A diode isconnected between the base and the emitter and poled in a direction sothat, when the transistor is forward biased, the diode isreverse-biased. Upon failure of the controlling voltage, current fromthe voltage divider flows through the diode, creating a small voltagedrop across the diode, suflicient to reverse-bias the base of thetransistor, thereby causing current to cease to flow through thetransistor. The controlled voltage, therefore, is removed, and remainsremoved until the reinitiation of the controlling voltage.

Additional objects and advantages of this invention, together with itsconstruction and mode of operation, will be more apparent from thefollowing description, when read in connection with the accompanyingdrawing which illustrates one embodiment of a control circuit inaccordance with this invention, together with a typical load circuit.

Referring to the sole figure, the control circuit It includes a PNPtransistor 12 having an emitter 14, a collector l6, and a base 18. Thecollector 16 is coupled to one end of a load resistor 17 having itsother end coupled to a source of constant reference potential, such asground. The emitter 14 is connected to a cathode 2i? of a diode 22having its anode 24 connected to the base 18 of the transistor 12. Avoltage divider comprising a pair of connected resistors 26 and 28 hasits common connection coupled to the base 18 of the transistor 12. Thecontrol circuit 10 has a pair of input terminals 30 and 32 connected,respectively, to the emitter 14 of the transistor 12 and to the voltagedivider at the resistor 26. A controlling voltage terminal 34 isconnected to the voltage divider at the resistor 28. The controlledvoltage terminal 36 is connected to the collector 16 of the transistorT2.

A power supply 33 is adapted to provide a plurality of output voltagesfor operation of both the control circuit ill and the load circuit 5%The voltage to be controlled (in the embodiment shown, volts) isconnected to the input terminal 3d. A voltage of +200 volts is connectedto the input terminal 32. The con trolling voltage 90 volts is connectedthrough a fuse id, or other impedance subject to failure, to a line 42..The controlling voltage input terminal 34 of the control circuit fill isconnected to the load circuit Ed by the line 42. The controlled voltageterminal 36 is connected to the load circuit Si) by means of a wire 44.

Different types of load circuits can be used in conjunction with thecontrol circuit. To illustrate the utility and advantages of theinvention, a transistor flip-flop circuit is shown as the load circuit50. The load circuit 5 as shown, includes a PNP transistor 52, having anemitter 54, a collector 56, and a base 58. The emitter 54 is connectedto a point of constant reference potential, such as ground. A similarPNP transistor 6t), having an emitter 62, a collector 64, and a base 66,has its emitter 62 coupled to the source of constant current potential,such as ground. Collector resistors 68, are

connected, respectively, to the collectors 56, 6d of the transistors 52,6h. The power supply 3% supplies constant voltage of approximately 10volts to the collector resistors 68, "7d by means of a line '72. A base.

biasing resistor 74 connects the base 53 of the transistor 52 to the +35volts controlled voltage line 44. A base resistor 7d further connectsthe base 58 to one end of a resistor 73 having its other end connectedto the volts controlling voltage line 42. The 90 volts controllingvoltage line 42 is connected to one end of a resistor 8d, which resi torhas its other end connected to one end of a base resistor (52, the otherend of the base resistor 82 being connected to the base 66 of thetransistor 6%. A base biasing resistor 34 connects the base as of thetransistor as to the +35 volts controlled voltage line 44.

A diode dd has its cathode 3% connected to the common connection of theresistors 76, 73, and has its anode git connected to (the collector 64of the transistor 60. in similar fashion, a diode d2 has its cathode 9connected to the common connection of the resistors 80, 8'2, and has itsanode 96 connected to the collector 5d of the transistor 52. A blufiingdiode 93 has its cathode connected to the cathode M of the diode 92, andhas its anode 102 connected toa set terminal 194% Likewise, a diode 1%has its cathode 168 connected to the cathode $8 of the diode 86, and hasits anode 11% connected to a reset terminal 112. The flip-flop circuit50 operates in a normal manner, whereby, when one tran- 3 sister 52, 60conducts, the other is non-conducting. The state of the ilip-fiopcircuit 50" may be changed by applying a positive pulse to theappropriate set or reset terminals 104, 112.

With the potentials described, and wit the typical values of resistorsand transistors as described hereinaiter, the potentials at the base 58and the base as of the transistors 52, are +2 volts and 8 volts,respectively, during one state of normal operation. During the otherstate of normal operation, the potentials at these points are 8 voltsand +2 volts, respectively.

The reverse bias of one of the transistors 52 or 60 is approximately 2volts between base and emitter. If, however, the fuse 4-0 should fail,or for some reason the controlling voltage line 42 should abnormallyapproach zero-potential, the potential applied to the base 53 or 66 ofthe transistor 52 or -60 tends to approach +35 volts with respect to theemitters 5 or 62. But for this invention, when the voltage applied tothe line 44 is +35 volts and the voltage on the line 42 is Zero volts(such as caused by a failure of the :fuse 40), the potential +35 voltsoccurs at base 58. The emitter 54 of the transistor 52 is connected toground. This reverse or back bias of +35 volts is suificient to damagethe transistor 52, 60, thereby destroying the utility of the loadcircuit 50. As a safeguard, however, as described iereinafter,applicants circuit :10, upon a drop of voltage or short circuit on theline 42, provides no output on the line 44-.

The power supply 38 supplies +35 volts, through the terminal 30, to theemitter 14 of the transistor 12. The potential, therefore, at theemitter 14 of the transistor 12 remains constant at +35 volts. The powersupply 38 also provides +200 volts to the terminal 32, and +90 volts,through a fuse 40, by means of the line 42 to the terminal 34. The +200volts and -90 volts at the terminals 32 and 34 are connected to avoltage divider 26, 23 so that the common connection of the resistors26, 28 is at a potential of approximately +34 volts. The +3 r voltspotential is coupled to the base 18 of the transistor '12, and the base18 being negative with respect to the emitter 14, causes forward currentconduction through the transistor 12 so that the potential at thecollector 16 of the transistor 12 is approximately +35 volts. Becausethe anode 24 of the diode 22 is negative with respect to the cathode ofthe diode 22, no current flows through the diode 22. Therefore, innormal operation, current from the +35 volts terminal from the powersupply 38 enters the terminal passes through the transistor 12, developsa voltage across the load resistor -17, and thus provides an outputcurrent at the terminal 36 which has a potential of approximately volts.When, due to abnormal operation, or other reason, the fuse 4'0open-circuits (or otherwise the voltage applied to the terminal 34approaches zero), the base 18 of the transistor 12 tends to become morepositive due to the +200 volts potential applied to the terminal 32.Current flows from the power supply 38, from the +200 volts source,through the terminal .32, and the resistor 26, to the anode 24 of diode22. The anode 24, being at a higher potential than the cathode 20,causes current to fiow through the diode 22. Because the diode '22 is alow potential device, the voltage drop across the diode 22. is on theorder of approximately one volt. This one volt-differential across thediode Z2 is sufficient, however, to apply a back bias of one voltbetween the emitter 14 and the base 18 of the transistor 12, therebycausing the transistor d2; to cease to conduct. The output terminal 36,connected to the collector 16 of the transistor 12, is, therefore, atground potential.

Upon replacement of the fuse 40 and upon eliminating the failure causingcondition, the voltage applied on the line 42. again becomes 90 volts.This voltage is sufiicient to again turn on the transistor 12 causingconduction hcrethrough, thereby providing an outof +35 volts upon theline' id.

novel control circuit 10 has many advantages. The circuit can he used,as described hereinabove, for controlling bias voltages of transistorloads. The control circuit l0 can be as a gating circuit or as abistable circuit, the output applied to the line 24 being controlled bythe voltage applied on the line 42.

illustrated below are typical values of components used in oneembodiment of the invention and for a typical load circuit. Other valuesmay be used without digressing from the scope of this invention.

Various modifications may be made to the circuits which are within thespirit of applicants invention. For example, the transistor and diodemay be opposite conductivity types so that .a positive controllingvoltage may operate upon a negative controlled voltage.

What is claimed is:

1. A means for receiving a first voltage to be controlled; a secondmeans for receiving a second voltage; a third means 'for receiving athird voltage, said third voltage being subject to abnormal operation; apair of resistors directly connected to each other in a seriesrelationship, the connection of said resistors defining a commonjunction terminal, one end of said pair of resistors bein connected tosaid second means, and the other end of said pair being connected tosaid third means; unilateral conducting means coupling said first meansto said junction terminal; a load circuit; and a transistor having oneelectrode coupled to said junction terminal, a second electrode coupledto said first means, and a third electrode connected to said loadcircuit; said third means being directly connected to said load circuit.

2. In combination, a power supply adapted to provide a plurality ofvoltages, a control circuit and a load circuit, said power supply,control circuit and load circuit being interconnected with one another;said load circuit comprising means for utilizing a first and secondvoltage concurrently, said load circuit upon abnormal failure of saidfirst voltage requiring said second voltage to be terminated in order.to prevent destruction thereto; said control circuit comprising anamplifier having input, output and control electrodes, said outputelectrode being adapted to provide said second voltage, said inputelectrode being connected to said power supply, impedance moans directlyconnecting said control electrode to said load circuit for providingsaid first voltage, second impedance means directly connecting saidcontrol electrode to said power supply, unilateral conducting meansdirectly connected between said input and control electrodes, saidunilateral conducting means being poled in a direction to conduct whensaid amplifier is non-conducting and to cease to conduct when saidamplifier is conducting.

3. in combination, a power supply adapted to provide a plurality ofvoltages, a control circuit and a load circuit, said power supply,control circuit and load circuit being interconnected with one another,said load circuit comprising means for utilizing a first and secondvoltage concurrently, said load circuit upon abnormal failure of saidfirst voltage requiring said second voltage to be terminated in order toprevent destruction thereto, said control circuit comprising atransistor having input, output and control electrodes, said outputelectrode being adapted to provide said second voltage, said inputelectrode being connected to said power supply, impedance means directlyconnecting said control electrode to said load circuit for providingsaid first voltage, second impedance means directly connecting saidcontrol electrode to said power supply, unilateral conducting meansdirect ly connected between said input and control electrodes, saidunilateral conducting means being poled in a direction to conduct in adirection opposite to the direction of conductivity of said transistor.

4. In combination, a power supply adapted to provide a plurality ofvoltages, a control circuit and a transistor load circuit, said powersupply, control circuit and transistor load circuit being interconnectedwith one another, said transistor load circuit comprising means forutilizing a first and second voltage concurrently, said transistor loadcircuit upon abnormal failure of said first voltage requiring saidsecond voltage to be terminated in order to prevent destruction thereto,said control circuit comprising transistor having input, output andcontrol electrodes, said output electrode being adapted to provide saidsecond voltage, said input electrode being connected to said powersupply, impedance means directly connecting said control electrode tosaid transistor load circuit for providing said first voltage, secondimpedance means directly connecting said control electrode to said powersupply, unilateral conducting means directly connected between saidinput and control electrodes, said unilateral conducting means beingpoled in a direction to conduct in a direction opposite to the directionof conductivity of said transistor.

References Cited in the file of this patent UNITED STATES PATENTS2,874,312 Radcliffe et a1. Feb. 17, 1959 2,876,367 Summer Mar. 3, 19592,891,726 Decker et a1 June 23, 1959 2,904,678 Malchow Sept. 15, 19592,931,920 Baker Apr. 5, 1960 2,947,950 Pinckaers Aug. 2, 1960 2,949,543Nordahl et al Aug. 16, 1960 2,978,595 MacKay Apr. 4, 196 1

2. IN COMBINATION, A POWER SUPPLY ADAPTED TO PROVIDE A PLURALITY OFVOLTAGES, A CONTROL CIRCUIT AND A LOAD CIRCUIT, SAID POWER SUPPLY,CONTROL CIRCUIT AND LOAD CIRCUIT BEING INTERCONNECTED WITH ONE ANOTHER;SAID LOAD CIRCUIT COMPRISING MEANS FOR UTILIZING A FIRST AND SECONDVOLTAGE CONCURRENTLY, SAID LOAD CIRCUIT UPON ABNORMAL FAILURE OF SAIDFIRST VOLTAGE REQUIRING SAID SECOND VOLTAGE TO BE TERMINATED IN ORDER TOPREVENT DESTRUCTION THERETO; SAID CONTROL CIRCUIT COMPRISING ANAMPLIFIER HAVING INPUT, OUTPUT AND CONTROL ELECTRODES, SAID OUTPUTELECTRODE BEING ADAPTED TO PROVIDE SAID SECOND VOLTAGE, SAID INPUTELECTRODE BEING CONNECTED TO SAID POWER SUPPLY, IMPEDANCE MEANS DIRECTLYCONNECTING SAID CONTROL ELECTRODE TO SAID LOAD CIRCUIT FOR PROVIDINGSAID FIRST VOLTAGE, SECOND IMPEDANCE MEANS DIRECTLY CONNECTING SAIDCONTROL ELECTRODE